Is it possible to have a gunsmith take the barrel from a model 67 and install it on a 686 or 686 plus? Essentially I'm looking to have something that looks like a model 15 that fires .357 and hot .38s.

Hello Esquire, not very practical. The the K frame barrel shank /thread diameter is a bit too small. That is one area where the L-frame was specifically beefed up to handle continuous use of .357 ammo (125 grain was reported to be the major culprit), and avoid potential cracking of the forcing cone. A 686 Mountain Gun barrel, might give the look you want. I also saw photos somewhere, possibly on this forum, of a 686 barrel machined to look more like some of the K frame barrels, part underlug, rather than full underlug. Perehaps a 681 barrel from the fixed sighted version on the L-frame? Would need a taller front sight though to work with the adjustable rear sight. There is someone on the forum who is quite knowledgeable about changing around L- frame barrels, but it's late here and sorry, can't remember his user name at the moment. ymmv

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NRA Life, COTEP 640

What you want is the same thing I'm looking for, a model 620, it's a L frame with what looks like a 66 or 67 barrel. Also looks like a 686 Mountain gun. I think S&W is really missing the boat by not making more of these.

Correct. I did some additional research after posting last night and found out about the models 619 and 620. My question now is what would be more cost effective/practical. Getting a 620 and grinding down the underlug to look like the 619 or putting a 619 barrel on a 620 then installing the 620 front sight on said barrel.

The 620 uses a 2 piece barrel and the barrel shroud is "keyed" to the frame. I suspect that the placement of that "key" is in the underlug, so by cutting away you'd be cutting away the "key" that prevents the barrel shroud from rotating.

A better option, although more expensive, would be to purchase a 686 Mountain Gun and machining the barrel to the profile you desire. About 6 months ago Lipsey's was still listing the 686 Mountain gun so they may still have some in stock. BTW, the 686 Mountain Gun featureds a Tapered barrel, so even with the half lug it starts out with a barrel that is very similar to a Tapered Barrel model 15 or 67. Since the 686 features a one piece barrel that isn't keyed to the frame, it would be a rather simple task for a talented gunsmith to re-profile the barrel to the look you desire.

PS; if it weren't for budgetary constraints I'd have one of those 686 Mountain guns myself in spite of that awful billboard sized laser engraving on the barrel. Fact is that I find my older tapered barrel model 67 to have the best balance of any revolver I've ever shot and I expect a tapered barrel semi lugged 4 inch 686 would come very close to having that perfect balance. I'll also note that I own a 620 and find it's accuracy to be stunning, however the balance is only so-so compared to my 67-1.